The present invention relates to a photothermographic material, in particular, a photothermographic material for scanners and image setters, which is suitable for photomechanical processes. More precisely, the present invention relates to a photothermographic material that shows low fog and high Dmax (maximum density) and can be stored for a long period of time after development.
A large number of photosensitive materials are known which have a photosensitive image-forming layer on a support and form images by exposing imagewise. Among such materials, as an example of a system that contributes to environmental protection or enables simplification of image formation means, there is a technique of forming an image by heat development.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photomechanical processes from the standpoints of environmental protection and space savings. Therefore, techniques relating to photothermographic materials for use in photomechanical processes are required to be developed, which enables efficient exposure by a laser scanner or a laser image setter and formation of a clear black image having high resolution and sharpness. Such photothermographic materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904, 3,457,075 and D. Klosterboer, Imaging Processes and Materials, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, 8th ed., Chapter 9, page 279, compiled by J. Sturge, V. Walworth and A. Shepp, Neblette (1989). Such a photothermographic material contains a reducible non-photosensitive silver source (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount, and a reducing agent for silver, which are usually dispersed in an organic binder matrix. The photosensitive material is stable at an ambient temperature, but when the material is heated at a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced by the reaction of the reducible silver salt in the exposed region shows black color and this presents a contrast to the non-exposed region to form an image.
In many of conventionally known photothermographic materials, an image-forming layer is formed by coating a coating solution using an organic solvent such as toluene, methyl ethyl ketone (MEK) and methanol as a solvent. However, not only use of an organic solvent as a solvent adversely affect human bodies during the production process, but also it is disadvantageous in view of cost because it requires process steps for recovery of the solvent and so forth.
Accordingly, methods of forming an image-forming layer by coating a coating solution using water as a solvent have been proposed. For example, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 49-52626, JP-A-53-116144 and so forth disclose image-forming layers utilizing gelatin as a binder, and JP-A-50-151138 discloses an image-forming layer utilizing polyvinyl alcohol as a binder. Furthermore, JP-A-60-61747 discloses an image-forming layer utilizing gelatin and polyvinyl alcohol in combination. As another example, JP-A-58-28737 discloses an image-forming layer utilizing a water-soluble polyvinyl acetal as a binder. If these binders are used, image-forming layers can be formed by using a coating solution comprising an aqueous solvent, and therefore considerable merits can be obtained with respect to environment and cost.
However, when a polymer such as gelatin, polyvinyl alcohol or water-soluble polyacetal is used as a binder, silver tone of developed areas becomes brown or yellow, which quite differs from black color regarded as a preferred proper color, and in addition, there arises, for example, a problem that the blacking density in exposed areas is low and the density in unexposed areas is high. Thus, there can be obtained only images of which commercial value is seriously impaired.
European Patent Laid-open Publication (hereinafter referred to as EP-A) 762,196, JP-A-9-90550 and so forth disclose that high-contrast photographic property can be obtained by incorporating Group VII or VIII metal ions or metal complex ions into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photosensitive materials. However, use of such a binder used in a coating solution comprising aqueous solvent as described above in combination with a nucleating agent such as hydrazine suffers from a drawback that it is likely to invite fog, while it provides images of high contrast. Further, the aforementioned heat development system suffers from a problem that fog is more likely to increase when a photosensitive material is stored for a long period of time after heat development compared with conventional photosensitive materials treated with chemicals.
Therefore, there has been desired a technique for providing a photothermographic material that shows low fog and high Dmax (maximum density) and exhibits little increase of fog even after the photosensitive material is stored for a long period of time.
Accordingly, an object to be achieved by the present invention is to solve the aforementioned problems of the prior art. That is, the first object of the present invention is to provide a photothermographic material, in particular, for photomechanical processes, more specifically, for scanners and image setters, which shows low fog and high Dmax (maximum density), and exhibits little increase of fog even after the photosensitive material after development is stored for a long period of time.
Further, the second object to be achieved by the present invention is to provide a photothermographic material that can be produced by coating of aqueous system, which is advantageous in view of environmental protection and cost.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that a superior photothermographic material showing the desired effect can be obtained by using a nucleating agent and a surfactant having a particular structure in combination in a photothermographic material, and thus accomplished the present invention.
That is, the present invention provides a photothermographic material containing a non-photosensitive silver salt, a photosensitive silver halide and a binder on a support, which comprises a nucleating agent and a surfactant represented by the following formula (F):
[Rf-(Rc)n]m-Zxe2x80x83xe2x80x83Formula (F):
In the formula, Rf represents a perfluoroalkyl group, Rc represents an alkylene group, and Z represents a group having an anionic group, cationic group, betaine group or nonionic group required for imparting surface activity, n is 0 or 1 and m is 1, 2 or 3.
According to the present invention, there is provided a photothermographic material that shows photographic properties suitable for photomechanical process, that is, low fog, high Dmax (maximum density), and little increase of fog even after the photosensitive material after development is stored for a long period of time. Further, the photothermographic material of the present invention can be produced by coating of aqueous system, which is advantageous in view of environmental protection and cost.